The present invention relates to a bearing support stand for rotating shafts.
Especially when bearing supports for blowers are involved, such support stands are made as rigidly as possible, and ordinarily of sheet metal construction. The supporting plates for both the fixed and the loose bearing are connected as rigidly as possible to the foundation, or, with machines mounted on shock absorbers, on the common frame. In all axes and planes, even with larger unbalancing forces, only minimum displacements of the supporting plates relative to the foundation or the frame should occur.
Axial forces in the shaft direction only stress the fixed bearing. Thermal expansions of the shaft are absorbed in the loose bearing without appreciable force effects. This would require, however, that the loose bearing is either a sliding bearing without axial restriction or a cylinder roller bearing or needle bearing without rims. Usually, self-aligning roller bearings are used. It is assumed that the loose bearing system is displaced in its housing during thermal expansion of the shaft.
Depending on the ratio of radial load to axial load, with a self-aligning roller bearing, both roller rows carry different portions of the load, with the bottom rollers carrying the most load.
If the loose bearing system is to be displaced axially within the housing, the friction force between outside ring and the housing must be overcome. Hence, displacement requires an axial force which at least equals the calculated friction force. Depending on the friction between outer ring and housing and the degree of swing owing to non-axial symmetrical force distribution of friction force and axial load, one must expect axial loads during displacement of the loose bearing which may increase to whole multiples of the radial load.
An advance calculation of the displacement force is not possible. For blowers with changing shaft temperatures, one must assume that loose and fixed bearings run continuously with axial loads of unknown size because after displacement of the loose bearing outer ring, there will appear an equilibrium between displacement force on the one hand and elastic forces of the bearing and of the substructure on the other hand.
From a vibration analysis viewpoint, the bearings couple the rotor to the support stands and hence also to the frame or to the foundation. With self-aligning roller bearings, the degree of coupling depends largely on the ratio of axial load to radial load. It ranges from relatively loose coupling with pure axially non-loaded loose bearings to relatively rigid coupling with axially overloaded bearings where all rollers of one row are engaged. This results for the overall system rotorsupport stand--foundation in different resonant frequencies which cannot be calculated in advance with sufficient accuracy and which depend on the prevailing axial load and hence also on the shaft temperature.
It is an object of the present invention to avoid these disadvantages and to calculate the forces occurring in the bearing more accurately by a special construction of the bearing support stand.
Another object of the present invention is to provide a bearing support stand of the foregoing character which is substantially simple in construction and may economically fabricated.
A further object of the present invention is to provide an arrangement, as described, which may be easily maintained in service and which has a substantially long service life.